This invention is directed generally to friction retard feeders, and more particularly, to an improved nudger for use is such feeders.
Traditionally, nudger rolls are employed in friction retard feeders to move the top substrate(s) from a stack to a retard mechanism as a result of a net frictional force. The retard mechanism allows a single substrate at a time to pass through the mechanism. Some nudger rolls are constructed from an elastomeric material. These rolls have a failure mode of loss of a suitably high friction coefficient due to contamination, dirt build-up and wear. Other nudger rolls are in the form of a series of metal pin wheels which act to grab or stick the top sheet in the stack and move it into the friction retard mechanism. A studded roll of this type works well for most substrate types, and has a long roll life. However, the studded roll does not handle high density substrates very well due to an ability to penetrate the substrate surface. Also, the studded roll does not handle transparencies satisfactorily. Further, the studded roll may leave scratch marks on the surface of substrates fed at high feed rates.
When a rotating roll is used to feed the paper by the frictional force between them, the maximum available feed force is determined by the product of the normal force and the coefficient of friction between the roll and the substrate which could be paper, transparencies, etc. Because the coefficient of friction is uncertain in nature, the maximum available feed force is mainly controlled by the normal force. That is, as the required feed force increases, the normal force is also set to a larger value. In most machines that use nudger rolls as feed rolls, the normal force is set to a fixed optimum value to meet the particular design requirements. But there may still appear a failure, such as misfeed, as the design environment changes. Attempts at overcoming these nudger roll deficiencies include U.S. Pat. No. 3,866,903 which discloses a sheet feeding apparatus that delivers a top sheet of a stack to advancing rolls by using a cylindrical sleeve comprised of an elastomeric material with a high coefficient of friction. The sleeve is rotated by a drive to move the top sheet towards the advancing rolls. A device for separating single textile workpieces from the top of a stack is shown in U.S. Pat. No. 4,157,825 that includes a holding member having holding pins and a rotatable member having a plurality of radially extending bristles. The holding member causes an engagement of the topmost workpiece with the pins. The rotatable member directs the topmost workpiece. A pair of nudger rolls are disclosed in U.S. Pat. No. 4,928,948 for urging a sheet toward feed rolls that are on the same centerline in the feed direction. A hybrid nudger roll is disclosed in U.S. Pat. No. 5,149,077 for use in a friction retard feeder that includes alternating elastomeric and studded rolls positioned on a support shaft. The outer surface of the elastomeric rolls extends beyond the tips of the studded rolls, but when the elastomeric rolls are deformed against a stack of sheets due to normal force, the tips of the studded rolls extends beyond the outer surface of the elastomeric rolls. Even with availability of the abovementioned nudger rolls, the need still exists for a nudger roll useful in retard feeders for shingling a wide variety of substrates which can adjust the normal force as the requirements for the feed force changes.
Accordingly, in an aspect of this invention, a self-adjusting nudger roll is disclosed which comprises two rolls held together by a spring with one of the rolls being fixedly attached in a position while the other acts as a rotating feed roll and simultaneously orbit about the surface of the one roll. The assembly automatically adjusts the normal force on substrates as the requirement of the feed force changes and thereby reduces misfeeds and multifeeds.